[clang] [CIR] Add support for thread-local storage (TLS) (PR #168662)

[Andy Kaylor via cfe-commits]

================
@@ -1933,6 +1902,35 @@ void CIRGenModule::setGVPropertiesAux(mlir::Operation *op,
   assert(!cir::MissingFeatures::opGlobalPartition());
 }
 
+cir::TLS_Model CIRGenModule::GetDefaultCIRTLSModel() const {
+  switch (getCodeGenOpts().getDefaultTLSModel()) {
+  case CodeGenOptions::GeneralDynamicTLSModel:
+    return cir::TLS_Model::GeneralDynamic;
+  case CodeGenOptions::LocalDynamicTLSModel:
+    return cir::TLS_Model::LocalDynamic;
+  case CodeGenOptions::InitialExecTLSModel:
+    return cir::TLS_Model::InitialExec;
+  case CodeGenOptions::LocalExecTLSModel:
+    return cir::TLS_Model::LocalExec;
+  }
+  llvm_unreachable("Invalid TLS model!");
+}
+
+void CIRGenModule::setTLSMode(mlir::Operation *op, const VarDecl &d) const {
+  assert(d.getTLSKind() && "setting TLS mode on non-TLS var!");
+
+  auto tlm = GetDefaultCIRTLSModel();
----------------
andykaylor wrote:

```suggestion
  cir::TLS_Model tlm = getDefaultCIRTLSModel();
```
Even though the function definition is right above here currently, I don't think we want to use `auto` here.

https://github.com/llvm/llvm-project/pull/168662